For swivel-type work machines, such as an excavator or a crane, there has been known a technique of employing an electric motor as a swivel driving source, in place of a traditional hydraulic motor, as disclosed in the following Patent Publication 1.
This conventional technique uses the electric motor also as a power generator to brake/stop a revolving superstructure by a regenerative braking torque from the power generating action.
[Patent Publication 1] Japanese Patent Laid-Open Publication No. 2001-207478
In the event of a malfunction such that power supply to the swiveling electric motor is interrupted due to a failure of a power generator, etc., or the swiveling electric motor becomes out of control due to a failure in a swivel control system, the above conventional technique will involve a situation where only inertia of the revolving superstructure acts on the electric motor as with a neutral free mode in a hydraulic motor-based system, without any braking based on the power generating action of the electric motor, and it will take time to stop the revolving superstructure.
A shovel or crane is also equipped with a mechanical brake serving as a stop-holding parking brake in a rotationally stopped state. Thus, it is contemplated to allow the mechanical brake to be activated as an emergency brake.
However, the mechanical brake originally has only a brake performance designed for a stop-holding brake. Therefore, if the mechanical brake is activated during a high-speed rotation, it is likely to be damaged due to lack of its own heat capacity. Providing the mechanical brake with a sufficient heat capacity, requires a cooling device, etc., which increase a size of the entire mechanical brake. That results in poor practicality in terms of installation space and cost.